The present invention relates generally to communication systems and, more particularly, to a method and apparatus for completing a handover between wireless communication systems.
Communication systems consisting of land mobile radio, cellular radiotelephone, personal communication system (PCS), and various other types are well known. A typical multiple access wireless communication system such as a digital radio frequency (RF) radiotelephone system includes a base station system, (BSS), having one or more base station transmitters and receivers (BTSs), and at least one base station controller (BSC). The BSS communicates via an RF channel with a mobile communication unit, commonly referred to as a mobile station (MS), operating within a coverage area served by a BTS. The BSCs are linked to mobile switching centers (MSC) which provide a connection between the multiple access wireless communication system and the public switched telephone network (PSTN) as well as interconnection of various cellular radiotelephone communication systems. The MSC provides the switching function as well as call routing, call billing, and subscriber features, among other things, whereas the BSC provides mobility management functions such as mobile station registration, location updating, and handover in the multiple access wireless communication system.
One such multiple access wireless communication system, which may be referred to as a MSC-based architecture system, is a direct sequence code division multiple access (DS-CDMA) cellular communication systems, such as set forth in the TIA Interim Standard (IS)-95A, Mobile Station-Base Station Compatibility Standards for Dual-Mode Wideband Spread Spectrum Cellular Systems, Telecommunications Industry Association, Washington, D. C. July 1993 [IS-95A]. According to these standards, coded communication signals are transmitted in common 1.25 megahertz (MHz) carriers between the BSS and mobile stations that are communicating in the service coverage areas of the BSS.
Multiple access wireless communication system functionality may be also accomplished through an alternate architecture. Such an architecture, commonly referred to as Generic C architecture, utilizes an landline switch, for example, a class 5 service switching point (SSP), to provide the switching function for the wireless communication system, thereby mitigating the need for an MSC. The SSP may also serve to provide the connection between the Generic C wireless communication system and the PSTN.
In a Generic C wireless communication system, at least one base station system (BSS) is linked to the SSP. In addition in one configuration of a Generic C architecture, the SSP is in communication with a service control point (SCP). The SCP is a database, remotely located from the SSP, which communicates with the SSP to provide customer-specific information. The SCP, when queried by the SSP, provides information to the SSP via a access manager/visitor location register (AMNLR). The AMNLR which provides wireless communication system access to a landline switch may be remotely located or collocated with the SCP.
In a wireless communication system, a communication link via an RF channel is established between a mobile station, or subscriber unit, and a source, or serving, BSC. As a mobile station moves out of range of the source BSC, the signal quality degrades until the communication link is ultimately be broken, or the call xe2x80x9cdroppedxe2x80x9d. To avoid loss of the communication link resulting from a dropped call, the communication link is shifted from the source BSC to a target BSC. This process of making the shift is commonly referred to in the wireless communication system area as a handover process.
Communication system service providers as well as communication system users desire handover capability between wireless communication systems configured with different architectures. For example, a mobile station, having received a landline originated call while initially traveling in a wireless communication system served by a Generic C architecture, may require a handover of its communication signal to a wireless communication system served by a MSC-based architecture.
Implementing mobile station handover capability between two Generic C-based architecture wireless communication systems has been specified in standards. Furthermore, implementing mobile station handover capability between MSC-based architecture wireless communication systems has been specified in standards. But, implementing mobile station handover capability between a wireless communication system served by a Generic C-based architecture and a wireless communication system served by a MSC-based architecture has not been specified or designed.
However, it has been suggested that handover capability between a Generic C architecture wireless communication system and an MSC-based architecture wireless communication system be enabled via a trunking scheme. The trunking scheme suggested requires additional trunk groups to be setup between all BSC""s and all MSC""s. For example, if three MSCs were possible handover candidates associated with ten BSCs, thirty additional trunking groups, or Ti spans, would be required to be allocated and controlled between the BSCs and the MSCs, thus incurring additional costs to wireless communication system operators. Obviously, a more cost efficient method of enabling a handover capability of a mobile communication signal between two architecturally different wireless communication systems is desired.
Therefore, a need exists for a method and apparatus for completing a handover of a mobile communication signal between architecturally different wireless communication systems which overcomes problems associated with the prior art.